The present invention relates generally to filtering and thrombectomy devices and systems which can be used to capture embolic material or thrombi found in blood vessels. The filtering devices and systems of the present invention are particularly useful when performing balloon angioplasty, stenting procedures, laser angioplasty or atherectomy in critical vessels where the release of embolic debris into the bloodstream can occlude the flow of oxygenated blood to the brain or other vital organs, which can cause devastating consequences to the patient. The thrombectomy devices are suited for the removal of thrombus in a variety of vessels. While the embolic filtering and thrombectomy devices and systems of the present invention are particularly useful in the cerebral vasculature and neurovasculature, the inventions can be used in conjunction with any vascular interventional procedure in which there is an embolic risk.
A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the wall of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. In typical PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral artery and advanced to near the target vasculature. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially expand the atherosclerotic plaque of the lesion and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty. Another procedure is laser angioplasty which utilizes a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which cutting blades are rotated to shave the deposited plaque from the arterial wall. A vacuum catheter is usually used to capture the shaved plaque or thrombus from the blood stream during this procedure.
In the procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, as described above, through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
The above minimally invasive interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem which can become associated with all of these types of procedures, namely, the potential release of embolic debris into the bloodstream that can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient""s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, quite often particles are not fully vaporized and thus enter the bloodstream. Likewise, not all of the emboli created during an atherectomy procedure may be drawn into the vacuum catheter and, as a result, enter the bloodstream as well.
When any of the above-described procedures are performed in the vessels supplying blood to the brain, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Naturally occurring debris can also be highly dangerous to a patient. That is, debris which travels through the blood vessel as a natural result of bodily functions or disease states and not as a result of an intervention procedure. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments that naturally occur or that enter the circulatory system following vessel treatment utilizing any one of the above-identified procedures. One approach which has been attempted is the cutting of any debris into minute sizes which are unlikely to occlude major vessels within the patient""s vasculature. However, it is often difficult to control the size of the fragments which are formed, and the potential risk of vessel occlusion still exists, making such a procedure in the carotid arteries a high-risk proposition.
Other techniques which have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source which provides temporary suction to remove embolic debris from the bloodstream. However, as mentioned above, there have been complications with such systems since the vacuum catheter may not always remove all of the embolic material from the bloodstream, and a powerful suction could injure the patient""s vasculature or remove more blood than is safe. Other techniques which have had some limited success include the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. However, there have been problems associated with conventional filtering systems. In particular, certain previously developed filtering devices do not optimize the area for embolic collection. That is, conventional filtering devices may not present a collection device that spans the entity of the vessel or it may include supporting structure that itself impedes emboli collection. Certain other devices are not effective when used in conjunction with a microcatheter.
Moreover, thrombectomy and foreign matter removal devices have been disclosed in the art. However, such devices have been found to have structures which are either highly complex or lacking in sufficient or effective expansion and retraction capabilities. Disadvantages associated with the devices having highly complex structure include difficulty in manufacturability as well as use in conjunction with microcatheters. Other less complex devices can pull through clots due to in part the lack of experience in using the same, or lack an adequately fine mesh for capturing clots or foreign bodies.
Furthermore, systems heretofore disclosed in the art are generally limited by size compatibility and the increase in vessel size as the emboli is drawn out from the distal vascular occlusion location to a more proximal location. If the thrombectomy device is too large for the vessel it will not deploy correctly to capture the clot or foreign body, and if too small in diameter it cannot capture thromboembolic material or foreign bodies across the entire cross section of the blood vessel. Thus, a thrombectomy device that can be expanded to a relatively large diameter from a relatively small diameter is desirable as is the ability to effectively control such expansion and contraction.
What has been needed is a reliable filtering or thrombectomy device and system for use when treating blood vessels. The filter devices should be capable of filtering any naturally occurring embolic debris or that which may be released into the bloodstream during an interventional treatment, while minimizing the area occupied by structure supporting the filter so as to minimally obstruct blood flow, and safely contain the debris until the filtering device is removed from the patient""s vasculature. The thrombectomy devices should embody an expanded profile that completely occupies the vessel at the repair site as well as structure for effectively expanding and retracting the device. Moreover, such devices should be relatively easy to deliver through a microcatheter, as well as be deployed and removed from the patient""s vasculature and also should be capable of being used in narrow and very distal vasculature such as the cerebral vasculature. The following invention addresses these needs.
Briefly and in general terms, the present invention is directed toward expandable devices for repairing blood vessels. The expandable devices are particularly suited for removing emboli or thrombi from the bloodstream of a human or animal. One significant advantage provided by the present invention is the potential use of the expandable devices in narrow and very distal vasculature.
In one aspect of the invention, there is provided a loop with an embolic filter attached thereto. The loop is configured to self-expand generally perpendicularly to and optionally offset to a longitudinal axis of a delivery catheter. A tether is provided to effect the deployment from and withdrawal into the delivery catheter. The self-expandable loop and filter structure advantageously expands to occupy the entire cross-section of the lumen into which it is deployed. When the device is in its expanded configuration, the shape of the loop is defined by the lumen and the tether is positioned near a wall of the lumen.
In another aspect, the present invention includes multiple loops that are connected by longitudinally extending fibers. The connecting fibers may be crossing or non-crossing and may terminate at a superior loop or continue distally to define a tapered distal end. A catheter is provided for deploying the double loop device as is a tether which effectuates the delivery and withdrawal of the device. The multiple loops are intended to self-expand to occupy the entirety of the cross-section of the blood vessel into which it is deployed, the loops assuming the geometry of the vessel. Additionally, when the device is in its expanded configuration, the tether is intended to generally lie adjacent a wall defining the lumen thereby accomplishing less blood flow obstruction. The distal loops may also provide internal support for an embolic filter, facilitating material entry into the filter.
In a third aspect of the invention, an embolectomy snare is provided which has the advantage of being able to assume a very small profile when packed within a delivery catheter. The embolectomy snare is characterized by including a basket that is formed from non-overlapping elongate members.
In a fourth aspect of the invention, improved expansion control and a means for optimizing expansion profiles is incorporated into a thrombectomy device. In particular, one or more stops are provided on an elongate member to cause a basket-like thrombectomy device configured coaxially about the elongate member to thereby open and close the basket. By varying the weave pattern of the basket of the thrombectomy device, upon expansion of the same, a concavity can be formed, the same being particularly useful for engaging and removing clots from a blood vessel.
These and other objects and advantages of the invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings of illustrative embodiments.